Secondary thermal breaker



Sept. 13, 1949.

J, B. CLAPP SECONDARY THERMAL BREAKER Filed 0st. 30, 1945 INVENTOR. Jaw/7 5 [3e CAAPP A TTOP/Vf Y Patented Sept. 13, 1949 SECONDARY THERMAL BREAKER Jerome B. Clapp, North Plainfield, N. J asslgnor to The Thomas & Betts 00., Elizabeth, N. J., a

corporation of New Jersey Application October 30, 1945, Serial No. 625,551

3 Claims. (Cl. 200-113) The invention relates to a notice impellin signalling system for notifying a householder that he is over-loading his electric system and that he must disconnect some of the electrical appliances to bring the load within the capacity of his supply line, and incidentally relates to a device for providing protection to the secondary circuits of transformers not otherwise protected.

In accordance with present practices, electric current from the main line is led through street transformers to the house which is generally protected by safety fuses. It frequently happens that the householder introduces into the house circuits more electric appliances than was intended to be included in these hous circuits. Often the fuses either fail to function or the load on any one fuse is within its capacity. What is of concern in the instant situation is the total load on the line or lines leading from the street transformer int the house or houses supplied from a single transformer. An abnormally large number of electric devices fed from this line throws an over-load on the transformer with resulting burnin of the transformer or at least the actuation of a secondary breaker protecting the transformer. However, in either case the current is shut off from the house or houses, and it is necessary for the electric power company to send a man to restore the transformer to operative status. This of course involves expense, delay in the service, and in general, great inconvenience to all parties involved.

The primary object of the invention is to provide a signalling system for promptly notifying the householder that he or his neighbor i overloading his supply line and which system will continue to display visual danger signals so lon as the over-loaded condition persists, and incidentally to protect the street transformers from the effects of the over-load and also to help the householder find any defective instrument which may be causing the over-load.

More specifically defined, the invention features a device which will cause all of the household apparatus, including the lights, to go off and on every few seconds during the entire time the overload is present.

Broadly this objective is attained by incorporating in the supply line between the street transformer and the point or points where the local load is imposed a thermal bi-metallic circuit breaker of the type which functions by reason of the presence of an over-load current. A form of thermostatic snap action disc-calibrated to open on a predetermined over-load current, known as a Spencer disc, is admirably suited for the instant situation among other reasons because of its quick action. However, these Spencer devices even though they ma be provided with silver terminals do arc when moved to circuit breaking positions and are thus subject to all of the objectionable characteristics inherent in such arcing devices.

Further, snap switches of this kind return to their normal circuit closing conditions byreason of the cooling effect of the environmental temperatures which, of course, vary materially from time to time and thus the return of the circuit breaker to its closed position is apt to be irregular and of no particularly definite or dependable signalling value. It is the intent'of the present disclosure to cause these signals to function at definite regularly spaced-apart time intervals, that is, to cause the lights to go off for say thirty seconds, and then to come on for thirty seconds and so on a long as the over-load condition continues. The blinking of the lights can become quite irritating to the householder and thus compels him to find out what is causing the over-load.

In rural farming districts, it is a common practice for the farmer, and not infrequently for a group of farmers in the same location, to throw an abnormal load on his and their supply circuits during certain seasons of the year and certain times of the day and to do this without warning the power company supplying the community. Of course the power company prefers to maintain its supply load fairly constant, and is gearedv to meet weather and other knowing factors which govern its output. Another difficulty in rural communities especially where the customers are widely scattered is that it is not economically feasible to take a meter reading for power consumption every month and this is an expense which all companies have been endeavoring to avoid. The present disclosure contemplates the inclusion in each customers supply line of a load limiting device for preventing these peak overloads, and thus to assist the power companies to aviod the strain of providing for unanticipated overloads. As the power companies thus know the maximum possible supply allocated to each customer, it is possible by utilizing the invention herein featured to present each month an averaged bill, and then make a meter reading, say once a year to correct for the overcharge.

In order to allocate to each customer a maximum permissible consumption of power the present disclosure contemplates providing the power company with different sizes of controls, each set to operate at a preferred overload and the company installs that particular control best suited to the needs of each particular customer. In this way the permissible current consumption for any one customer may be changed from time to time as may be desired by the power company simply by making a substitution of one size of control for another on the street pole, and this can be done conveniently without otherwise affecting either the transformer on the pole or the lead-in wire to the customer's home.

Various other objects and advantages of the invention will be in part obvious from an inspection of the accompanying drawing and in part will be more fully set forth in the following particular description of one form of the invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the drawing:

Fig. 1 is a general view of a house representative of the usual two or three houses supplied from a single transformer illustrating in schematic outline a house circuit showing a preferred embodiment of the invention incorporated between the transformer and the house circuit;

Fig. 2 is an enlarged axial sectional view of the thermal circuit breaker device shown in side elevation in Fig. 1, showing the bi-metal thermal disk or bridge in full lines in its normal circuit closing position and in ghost lines showing the bridge in its circuit breaking position; and

Fig. 3 is a transverse sectional view taken on the line 33 of Fig. 2 looking downward as indicated by the arrows.

In the drawings there is shown a house A provided with a conventional electric wiring system B with the usual load developing apparatus, such as washing machine, ironer, toaster, radio, heaters, electric lights and the like, indicated collectively by the designation Load. The electric lights, one of which is marked C can be regarded when flickering or operating intermittently as hereinafter described as a notice impelling signalling device. The house circuit is supplied from a street transformer D mounted on a street pole E adjacent the house and connected thereto by a lead-in or customer's Wire F. While the disclosure is complete for one house, usually more than one house is supplied from each bracket below the transformer and accordingly it may be assumed that there is another house supplied from the companion lead-in wire F. As thus far described, the disclosure is intended to be conventional and is representative of any similar arrangement of protected circuits wherever the instant invention may be utilized.

The disclosure features the introduction into the secondary circuit including the line F leading from the transformer of a thermalcircuit breaker l in the illustrated case shown to be mounted on the outside of the transformer D.

The circuit breaker includes a receptacle formed of heat dissipating material, such as thin sheet steel. The receptacle includes an open top fluid tight tank l2 of cylindrical form provided with a closure l3 screwed tight onto the tank. The cover l3 and the bottom ll of the tank are provided, respectively, with axially aligned openings l5 and I5, in both of which are threaded bushings l6 of insulating material. A terminal rod I1 is inserted through the bushing closing the upper opening l5 and has its outer upper end secured electrically to the transformer by means of a secondary bushing clamp H! as is usual in such cases.

The lower end of the rod within the tank is provided on one side with a silver contact button l9. Similarly, an external lead in the form of a rigid rod 20, depends from the tank, extends through the bushing IS in the bottom I4, and terminates at its inner intruded end in spaced relation to the rod l1 and is likewise provided with a silver contact button 2|. The lead-in wire F is secured to the lower projecting end of the lead 20 by means of a screw clamp 22.

The circuit is normally closed between the contact buttons l9 and 2| by means of a thermal circult breaker 23 carried by and insulatedfrom a post 24 extending radially into the receptacle interior and projecting from the wall of the tank l2. The circuit breaker 23 is of the snap acting, bi-metal disc type calibrated to open on a predetermined overload current which causes the resistant heat acting expansively on the disk 25 to snap the same away from the fixed contacts I! and 2|, and automatically snaps itself in the opposite direction restoring itself to its normal circuit closing position when cooled. One such type of snap acting circuit breaker disc 25 now on the market is known as a "Spencer" thermostatic disc. In one form of this disc diametrically opposite points of its perimeter are provided with a pair of shiftable silver contacts 26 and 21 coacting respectively with the fixed contacts I 9 and 2|.

These thermal circuit closers, sometimes hereinafter called switches, come in different sizes and are differently calibrated. In each case that circuit closer is chosen which with its associates best suits the maximum load permitted on each particular transformer.

It is a feature of this disclosure that means be provided to insure a uniform time lag in each cooling cycle of the circuit breaker or switch following the heating thereof by the over-load current so that the cooling step be not seriously affected by the environmental temperatures exist'ing about its container. In order to obtain a uniform rate of heat discharge from the thermal disc in cooling the same, and thus to cause it to move back into its normal circuit closing position after a definite time lag, the circuit closer is embedded in a cooling medium capable of effecting a substantial uniform rate of cooling of the heated disc, when free of the over-load current passing therethrough. This cooling medium is preferably of liquid and homogeneous form and thus capable in flowing about in the receptacle to conduct the heat received from the switch quickly to the heat dissipating surface provided by the metal of which the receptacle is formed. It has been found that chlorinated diphenyl which is somewhat similar to arochlor, transil oil and other known form of liquids functioning as are extinguishing oils, operates efliciently for this purpose and oils of this character have the additional advantage of quenching any arcs which might tend to form on the breaking of the circuit. Chlorinated diphenyl has been used because it is heavier, that is, it has a greater thermal lag than the similar oils used in transformers at present. It is appreciated that if any of the lighter oils commonly used in the large transformer casings was used in the smaller volume casings herein featured, the liquid in the small casing would become heated more quickly than the liquid in the large transformers both being subjected to the same heating efiects incidental to the overload current passing therethrough. In order to maintain equality in temperature in both the small casing and in its associated transformer, and thus maintain what may be called a super thermal lag in the liquid about the switch, the heavier chlorinated diphenyl is prescribed.

It follows therefor that in designing the dimensions of the receptacle ll, care must be exercised in fixing the volume of the pool 29 and in the character of the liquid used to form the pool so as to obtain as near as possible the same thermal lag at the small receptacle II as is present in the associated transformer D. While chlorinated diphenyl is suggested as preferable, and has the advantage that it will last for a long time without the necessity of replenishing it, other forms of heat conducting and quenching materials are suggested for use in place of the oil, such for instance as boric acids in a saturant, or chlorine gas and the like. When the medium is a fluid, such as the liquid oil suggested, it is introduced into the receptacle through an inlet port 28 in the cover l3 and forms a pool 29 in which the thermal circuit breaker or switch is entirely submerged. The bottom 14 is provided with a drain off vent 30 for use in recharging the receptacle with fresh oil or other suitable liquid.

In operating and assuming that the aggregate number of household apparatus indicated by Load in the house and controlling or contributing to control the total load on the transformer secondary is below that for which the circuit breaker is set, the household apparatus including the lights which may be turned on at the time function conventionally and no signalling effects are present. However, if for any reason an overload current develops the resultant heating of the bi-metal disc 25 causes it to snap from the full line, circuit closed position, into the ghost line circuit broken position shown in Fig. 2, thus interrupting the current flow to the house. Of course any lit lights, as lamp C, will then go out. If during daylight use the householder becomes suspicions that any of the non-luminous apparatus is not working, he can turn on a few lights and wait a few seconds to see if they signal. Of course the disc would cool anyhow if left alone and would eventually snap back into its circuit closing position, but any such subsequent closing would be at random and could not be depended upon to constitute a signal. However, with the modulating liquid pool 29 acting to absorb the heat of the disc at auniform rate, the time delay in which the house circuit is open becomes more or less definite. In the illustrated embodiment of the invention, the disc was calibrated and the cooling capacity of the oil regulated by selecting the proper radial dimension and volumetric capacity of the pool to cause the lights, functioning as blinking signals, to go off for thirty seconds and on for thirty seconds, and again on for thirty seconds, and so on until the over-load condition is corrected.

While the device was functioning to provide the signals the heating of the transformer has been reduced substantially and most transformers can readily stand such over-loads for a limited time before their secondary winding starts to fail.

By utilizing a signalling device of this character the householders attention is called promptly to The cutting out of a defective heater, ironer, etc., not only eliminates the hazardous over-load on his home wiring system, but incidentally calls his attention to any particular apparatus which may be causing or contributing to an excessive overload condition. Under these circumstances, the electric light companies are not required, as at present to send a repair man to the scene to remedy the cause of the over-load and to reset the breaker on say a CSP transformer in the event the over-load has tripped it.

A standard form of transformer without secondary protection is quite liable to fail under the conditions of an over-load current present if it has no protection on its low side. The system herein featured provides a cheap form of protection on the low side of standard transformers now in general use.

I claim:

1. A thermal circuit breaker including a receptacle formed of a metal capable of discharging heat from the interior of the same into opposite sides of which receptacle projects a. pair of terminals provided exteriorly of the receptacle with readily detachable fastening means for con!- necting the terminals in circuit, each provided adiacent its inner end within the receptacle with a fixed silver contact, a bi-metal snap action disc supported at its center in the receptacle and provided at diametrically opposite points of its perimeter with a pair of silver contacts, normally engaging the fixed contacts to bridge the current therebetween, said disc calibrated to open on a predetermined overload current by reason of the resistant heating of the disc by such over-load current, said disc havin an inherent thermal time lag to remain open until cooled sufficiently to snap back into its normal circuit closing position and a liquid containin chlorinated diphenyl in the receptacle free to flow about the same and thus bring its heat into contact with the wall of the receptacle, and said liquid capable by reason ill the fact that something is wrong with his electric system and he knows that the trouble is in his own house or his neighbors home connected to the same transformer. The regular lighting and extinguishing of his house lights becomes a signal wherever they may be on anywhere in the house. He becomes educated to the necessity that he must reduce the load in order to stop the blinking.

of its capacity to receive and conduct heat acting to control the rate at which the disc cools and thus tending to insure constancy in the closing time lag substantially uninfluenced by variations in the ambient temperatures.

2. In a device of the class described, a heat dissipating metallic receptacle of cylindrical form having its exterior exposed for air-cooling, a pair of rods forming rigid conductors intruded into and insulated from the opposite ends of the receptacle whose outer ends beyond the receptacle are exposed for air-cooling, and having their adjacent ends spaced apart to form a gap at the axis of the cylinder, one of said conductors forming a lead provided with fastenin means for connecting it to a transformer, and the other conductor provided with means for connecting a. lead-in wire thereto, a bi-metal circuit breaker of the snap acting type supported by and insulated from a side of the receptacle, bridging the gap and biased to maintain itself in normal position closing the circuit between the rods, and said circuit breaker calibrated to open and thus momentarily break the circuit at the gap on a predetermined overload current through the circuit closer, a pool of quenching oil in the receptacle and in which pool the circuit breaker is immersed, said pool containing chlorinated diphenyl and said receptacle being otherwise free of any contents which might interfere with its capacity to cool its contents at a uniform rate.

3. A circuit breaker including a receptacle formed of a metallic cylinder whose outer surface atoms:

is exposed to the cooling eiiect of the ambient air and said cylinder provided at opposite ends with closures, a thermal circuit breaker oi the bimetal disk snap-action type supported by and insulated from the wall of the cylinder, a pair of terminal rods carried by and insulated from the closures extending along the axis or the cylinder and projecting from the receptacle to the exterior of the same and provided at their exterior portions with means for connecting them in circuit with associated devices, the circuit breaker being provided with a pair of diametrically related silver contact buttons, each of the rods provided adjacent its inner end with a silver contact button coacting with its companion on the circuit breaker to complete the circuit therethrough, and

a pool of chlorinated diphenyl in which all of the circuit breaker and the silver contact buttons in the rods are immersed and which pool functions to extinguish the arc and to impose a thermal lag en the path provided by the pool for conducting heat from the 6111:1119 breaker to the air-cooled suriaee oi the cylinder.

" JEROME B. CLAPP.

REFERENCES CITED The following references are of record in the flie oi this patent:

UNITED STATES PATENTS 

